(0) Summary

Within the Debian community there has been a
significant amount of concern about the GNU Free
Documentation License (GFDL), and whether it is, in
fact, a free license. This document attempts to
explain why Debian's answer is no.

It should be noted that this does not imply any
hostility towards the Free Software Foundation, and
does not mean that GFDL documentation should not be
considered free enough by others, and Debian itself
will continue distributing GFDL documentation in its
non-free section.

(1) What is the GFDL?

The GFDL is a license written by the Free Software
Foundation, who use it as a license for their own
documentation, and promote it to others. It is also
used as Wikipedia's license. To quote the GFDL's
Preamble:

The purpose of this License is to make a manual, textbook, or
other functional and useful document free in the sense of
freedom: to assure everyone the effective freedom to copy and
redistribute it, with or without modifying it, either
commercially or noncommercially. Secondarily, this License
preserves for the author and publisher a way to get credit for
their work, while not being considered responsible for
modifications made by others.

This License is a kind of copyleft, which means that
derivative works of the document must themselves be free in the
same sense. It complements the GNU General Public License, which
is a copyleft license designed for free software.

(2) How does it fail to meet Debian's standards for Free Software?

The GFDL conflicts with traditional requirements for free software in
a variety of ways, some of which are expanded upon below. As a copyleft
license, one of the consequences of this is that it is not possible to
include content from a document directly into free software under
the GFDL.

The major conflicts are:

(2.1) Invariant Sections

The most troublesome conflict concerns the class of invariant
sections that, once included, may not be modified or removed
from the documentation in future. Modifiability is, however, a
fundamental requirement of the DFSG, which states:

3. Derived Works

The license must allow modifications and derived works, and
must allow them to be distributed under the same terms as the
license of the original software.

Invariant sections create particular problems in reusing small
portions of the work (since any invariant section must be
included also, however large), and in making sure the
documentation remains accurate and relevant.

(2.2) Transparent Copies

The second conflict is related to the GFDL's requirements for
transparent copies of documentation (that is, a copy of the
documentation in a form suitable for editing). In particular,
Section 3 of the GFDL requires that a transparent copy of the
documentation be included with every opaque copy distributed, or
that a transparent copy is made available for a year after the
opaque copies are no longer being distributed.

For free software works, Debian expects that simply providing
the source (or transparent copy) alongside derivative works will
be sufficient, but this does not satisfy either clause of the
GFDL's requirements.

(2.3) Digital Rights Management

The third conflict with the GFDL arises from the measures in
Section 2 that attempt to overcome Digital Rights Management
(DRM) technologies. In particular, the GFDL states that You
may not use technical measures to obstruct or control the
reading or further copying of the copies you make or
distribute. This inhibits freedom in three ways: it limits
use of the documentation as well as distribution, by covering
all copies made, as well as copies distributed; it rules out
distributing copies on DRM-protected media, even if done in such
a way as to give users full access to a transparent copy of the
work; and, as written, it also potentially disallows encrypting
the documentation, or even storing it on a filesystem that
supports permissions.

(3) Why does documentation need to be Free Software?

There are a number of obvious differences between programs and
documentation that often inspire people to ask why not simply
have different standards for the two? For example, books are
often written by individuals, while programs are written by
teams, so proper credit for a book might be more important than
proper credit for a program.

On the other hand, free software is often written by a single
person, and free software documentation is often written by a
larger group of contributors. And the line between what is
documentation and what is a program is not always so clear
either, as content from one is often needed in the other (to
provide online help, to provide screenshots or interactive
tutorials, to provide a more detailed explanation by quoting
some of the source code). Similarly, while not all programs
demonstrate creativity or could be considered works of
art, some can, and trying to determine which is the case
for all the software in Debian would be a distraction from our
goals.

In practice, then, documentation simply isn't different enough
to warrant different standards: we still wish to provide source
code in the same manner as for programs, we still wish to be
able to modify and reuse documentation in other documentation
and programs as conveniently as possible, and we wish to be able
to provide our users with exactly the documentation they want,
without extraneous materials.

(4) How can this be fixed?

What, then, can documentation authors and others do about this?

An easy first step is to not include the
optional invariant sections in your
documentation, since they are not required by
the license, but are simply an option open to
authors.

Unfortunately this alone is not enough, as other clauses of the
GFDL render all GFDL documentation non-free. As a consequence,
other licenses should be investigated; generally it is probably
simplest to choose either the GNU General Public License (for a
copyleft license) or the BSD or MIT licenses (for a non-copyleft
license).

As most GFDL documentation is made available under the terms
of the GNU Free Documentation License, Version 1.2 or any
later version published by the Free Software Foundation,
the Free Software Foundation is able to remedy these problems by
changing the license. The problems discussed above require
relatively minor changes to the GFDL — allowing invariant
sections to be removed, allowing transparent copies to be made
available concurrently, and moderating the restrictions on
technical measures. Unfortunately, while members of the Debian
Project have been in contact with the FSF about these concerns
for the past four years, these negotiations have not come to any
conclusion to date.

This is the position of the Debian Project about the GNU Free
Documentation License as published by the Free Software
Foundation:

We consider that the GNU Free Documentation License version
1.2 conflicts with traditional requirements for free
software, since it allows for non-removable,
non-modifiable parts to be present in documents
licensed under it. Such parts are commonly referred
to as invariant sections, and are described in
Section 4 of the GFDL.

As modifiability is a fundamental requirement of
the Debian Free Software Guidelines, this
restriction is not acceptable for us, and we cannot
accept in our distribution works that include such
unmodifiable content.

At the same time, we also consider that works
licensed under the GNU Free Documentation License
that include no invariant sections do fully meet
the requirements of the Debian Free Software
Guidelines.

This means that works that don't include any
Invariant Sections, Cover Texts, Acknowledgements,
and Dedications (or that do, but permission to
remove them is explicitly granted), are suitable
for the main component of our distribution.

Despite the above, GFDL'd documentation is still
not free of trouble, even for works with no
invariant sections: as an example, it is
incompatible with the major free software licenses,
which means that GFDL'd text can't be incorporated
into free programs.

For this reason, we encourage documentation authors
to license their works (or dual-license, together
with the GFDL) under the same terms as the software
they refer to, or any of the traditional free
software licenses like the GPL or the BSD
license.

0: Summary

This is the position of Debian Project about the GNU Free
Documentation License as published by the Free Software Foundation:

We consider that works licensed under GNU Free
Documentation License version 1.2 do fully
comply both with the requirements and the
spirit of Debian Free Software Guidelines.

Within Debian community there has been a
significant amount of uncertainty about the GNU
Free Documentation License (GFDL), and whether
it is, in fact, a free license. This
document attempts to explain why Debian's answer
is yes.

1: What is the GFDL?

The GFDL is a license written by the Free Software
Foundation, who use it as a license for their own
documentation, and promote it to others. It is also
used as Wikipedia's license. To quote the GFDL's
Preamble:

The purpose of this License is to make a manual, textbook, or
other functional and useful document free in the sense of
freedom: to assure everyone the effective freedom to copy and
redistribute it, with or without modifying it, either
commercially or noncommercially. Secondarily, this License
preserves for the author and publisher a way to get credit for
their work, while not being considered responsible for
modifications made by others.

This License is a kind of copyleft, which means that
derivative works of the document must themselves be free in the
same sense. It complements the GNU General Public License, which
is a copyleft license designed for free software.

(2) The Invariant Sections — Main Objection
Against GFDL

One of the most widespread
objections against GFDL is that GFDL permits works
covered under it to include certain sections,
designated as invariant. The text inside such
sections can not be changed or removed from the
work in future.

GFDL places considerable constraints on the
purpose of texts that can be included in an
invariant section. According to GFDL all
invariant sections must be also secondary
sections, i.e. they meet the following
definition

A Secondary Section is a named
appendix or a front-matter section of the
Document that deals exclusively with the
relationship of the publishers or authors
of the Document to the Document's overall
subject (or to related matters) and
contains nothing that could fall directly
within that overall subject. [...] The
relationship could be a matter of
historical connection with the subject or
with related matters, or of legal,
commercial, philosophical, ethical or
political position regarding them.

Consequently the secondary sections (and in
particular the invariant sections) are allowed
to include only personal position of the
authors or the publishers to some subject. It
is useless and unethical to modify somebody
else's personal position; in some cases this
is even illegal. For such texts Richard
Stallman (the founder of the Free Software
Movement and the GNU project and author of
GFDL) says [1]:

The whole point of those works is that they
tell you what somebody thinks or what
somebody saw or what somebody believes. To
modify them is to misrepresent the authors;
so modifying these works is not a socially
useful activity. And so verbatim copying is
the only thing that people really need to be
allowed to do.

This feature of GFDL can be opposed to the
following requirement of Debian Free Software
Guidelines:

3. Derived Works

The license must allow modifications and
derived works, and must allow them to be
distributed under the same terms as the
license of the original software.

It is naive to think that in order to fulfil
this requirement of DFSG the free licenses have to
permit arbitrary modifications. There are several
licenses that Debian has always acknowledged as
free that impose some limitations on the permitted
modifications. For example the GNU General Public
License contains the following clause:

If the modified program normally reads
commands interactively when run, you must
cause it, when started running for such
interactive use in the most ordinary way, to
print or display an announcement including an
appropriate copyright notice and a notice that
there is no warranty (or else, saying that you
provide a warranty) and that users may
redistribute the program under these
conditions, and telling the user how to view a
copy of this License.

The licenses that contain the so called
advertising clause give us another example:

All advertising materials mentioning
features or use of this software must
display the following acknowledgement:
This product includes software developed
by ...

Consequently when judging whether some license
is free or not, one has to take into account what
kind of restrictions are imposed and how these
restrictions fit to the Social Contract of Debian:

4. Our priorities are our users and free software

We will be guided by the needs of our users
and the free software community. We will
place their interests first in our
priorities.

Currently GFDL is a license acknowledged as
free by the great mass of the members of the
free software community and as a result it is
used for the documentation of great part of
the currently available free programs. If
Debian decided that GFDL is not free, this
would mean that Debian attempted to impose on
the free software community alternative
meaning of free software, effectively
violating its Social Contract with the free
software community.

We should be able to improve the free
software and to adapt it to certain needs and
this stays behind the requirement of DFSG for
modifiability. GFDL allows everybody who
disagrees with a personal position expressed
in an invariant section to add their own
secondary section and to describe their
objections or additions. This is a
reasonable method to improve the available
secondary sections, a method that does not
lead to misrepresenting the authors opinion
or to censorship.

(3) Transparent copies

Another objections against GFDL is that
according to GFDL it is not enough to just put
a transparent copy of a document alongside
with the opaque version when you are
distributing it (which is all that you need to
do for sources under the GPL, for
example). Instead, the GFDL insists that you
must somehow include a machine-readable
Transparent copy (i.e., not allow the opaque
form to be downloaded without the transparent
form) or keep the transparent form available
for download at a publicly accessible location
for one year after the last distribution of
the opaque form.

The following is what the license says (the
capitalisations are not from the original
license):

You must either include a machine-readable
Transparent copy ALONG with each Opaque
copy, or state IN OR WITH each Opaque copy a
computer-network location from which the
general network-using public has access to
download using public-standard network
protocols a complete Transparent copy of the
Document, free of added material.

Consequently the license requires distribution
of the transparent form ALONG with each opaque
copy but not IN OR WITH each opaque copy. It
is a fact confirmed by Richard Stallman, author
of GFDL, and testified by the common practice,
that as long as you make the source and
binaries available so that the users can see
what's available and take what they want, you
have done what is required of you. It is up to
the user whether to download the transparent
form.

If the transparent copy is not distributed
along with the opaque copy then one must take
reasonably prudent steps to ensure that the
Transparent copy will remain accessible from
Internet at a stated location until at least
one year. In these circumstances the
requirement of GPL appears to be even more
severe — a written offer, valid for at least
three years, to give any third party a
complete machine-readable copy of the
corresponding source code.

(4) Digital Rights Management

The third objection against GFDL arises from
the measures in Section 2 that attempt to
overcome Digital Rights Management (DRM)
technologies. According to some
interpretations of the license, it rules out
distributing copies on DRM-protected media,
even if done in such a way as to give users
full access to a transparent copy of the work;
and, as written, it also potentially disallows
encrypting the documentation, or even storing
it on a file system that supports permissions.

In fact, the license says only this:

You may not use technical measures to
obstruct or control the reading or further
copying of the copies you make or distribute

This clause disallows the distribution or
storage of copies on DRM-protected media only
if a result of that action will be that the
reading or further copying of the copies is
obstructed or controlled. It is not supposed
to refer the use of encryption or file access
control on your own copy.

Consequently the measures of the license
against the DRM technologies are only a way
to ensure that the users are able to exercise
the rights they should have according to the
license. Because of that, these measures
serve similar purpose to the measures taken
in the GNU General Public License against the
patents:

If a patent license would not permit
royalty-free redistribution of the Program
by all those who receive copies directly or
indirectly through you, then the only way
you could satisfy both it and this License
would be to refrain entirely from
distribution of the Program.

We do not think that this requirement of GPL
makes GPL covered programs non-free even
though it can potentially make a GPL-covered
program undistributable. Its purpose is
against misuse of patents. Similarly, we do
not think that GFDL covered documentation is
non-free because of the measures taken in the
license against misuse of DRM-protected
media.